* refactor(storage): move type ByTagKey to the only package that uses it
* refactor(tsdb): use types in tsdb/cursors
* refactor(tsdb): remove unused type SeriesIDElems
* refactor(tsdb): inline only use of tsdb.ReadAllSeriesIDIterator
* refactor(tsdb): move series file to its own package
* refactor(storage): remove platform->influxdb aliases
Previously the series file did not include tombstones in the total
count. This commit now includes tombstones in the count as well as
fixes an issue where replayed tombstone records could exist but
their underlying ID did not exist. This caused the count to become
negative and with the count being `uint64` it caused the count to
rollover to `math.Uint64Max`.
I did this with a dumb editor macro, so some comments changed too.
Also rename root package from platform to influxdb.
In interest of minimizing risk, anyone importing the root package has
now aliased it to "platform" so that no changes beyond imports were
necessary in those files.
Lastly, replace the old platform module to local path /dev/null so that
nobody can accidentally reintroduce a platform dependency while
migrating platform code to influxdb.